Browsing by Subject "modulation"
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Item Fast amplitude and delay measurement for characterization of optical devices(Texas A&M University, 2006-10-30) Thompson, Michael ThomasA fast measurement technique based on the modulation phase-shift technique is developed to measure the wavelength-dependent magnitude and phase responses of optical devices. The measured phase response is in the form of group delay, which is used to determine the chromatic dispersion in the device under test by taking the derivative of the group delay with respect to optical wavelength. The measurement setup allows both step-tunable and sweeping laser sources. A modulation frequency of up to 2.7 GHz is accommodated. An alternate method for the phase measurement that overcomes non-linearities in the measurement setup is also presented. The speed of the measurement setup is limited by the sweeping speed of the laser source, which for the Agilent 81682A is 40 nm/sec. The magnitude accuracy is determined by taking a comparison to the commercially available Micron Finisar measurement system, where an error of 0.125 dB is noted. The phase accuracy of the measurement setup is tested by taking the Hilbert transform of the measured magnitude response of an Acetylene gas cell and comparing it to the integral of the measured group delay. The average deviation between the two methods is 0.1 radians. An Acetylene gas cell, fiber Bragg grating, and chirped Bragg grating are tested with the measurement setup and the Agilent 8168The characterization of the setup leads to the conclusion that the measurement setup developed in this paper is fast and accurate. The speed of the technique is on the order of microseconds for a single measurement and excels beyond the speed of the standard modulation phase-shift technique, which includes measurement times on the order of minutes. The accuracy of the technique is within 0.125 dB for magnitude measurements and 0.1 radians for phase measurements when compared to commercially available measurement systems.2A laser source at 40 nm/sec and the measurement plots are presented.Item High-Speed Link Modeling: Analog/Digital Equalization and Modulation Techniques(2012-07-16) Lee, KeytaekHigh-speed serial input-output (I/O) link has required advanced equalization and modulation techniques to mitigate inter-symbol interference (ISI) caused by multi-Gb/s signaling over band-limited channels. Increasing demands for transceiver power and area complexity has leveraged on-going interest in analog-to-digital converter (ADC) based link, which allows for robust equalization and flexible adaptation to advanced signaling. With diverse options in ISI control techniques, link performance analysis for complicated transceiver architectures is very important. This work presents advanced statistical modeling for ADC-based link, performance comparison of existing modulation and equalization techniques, and proposed hybrid ADC-based receiver that achieves further power saving in digital equalization. Statistical analysis precisely estimates high-speed link margins at given implementation constrains and low target bit-error-rate (BER), typically ranges from 1e-12 to 1e-15, by applying proper statistical bound of noise and distortion. The proposed statistical ADC-based link modeling utilizes bounded probability density function (PDF) of limited quantization distortion (4-6 bits) through digital feed-forward and decision feedback equalizers (FFE-DFE) to improve low target BER estimation. Based on statistical modeling, this work surveys the impact of insufficient equalization, jitter and crosstalk on modulation selection among two and four level pulse amplitude modulation (PAM-2 and PAM-4, respectively) and duobinary, and ADC resolution reduction performance by partial analog equalizer (PAE). While the information of channel loss at effective Nyquist frequency and signaling constellation loss initially guides modulation selection, the statistical analysis results show that PAM-4 best tolerates jitter and crosstalk, and duobinary requires the least equalization complexity. Meanwhile, despite robust digital equalization, high-speed ADC complexity and power consumption is still a critical bottleneck, so that PAE is necessitated to reduce ADC resolution requirement. Statistical analysis presents up to 8-bit resolution is required in 12.5Gb/s data communications at 46dB of channel loss without PAE, while 5-bit ADC is enough with 3-tap FFE PAE. For optimal ADC resolution reduction by PAE, digital equalizer complexity also increases to provide enough margin tolerating significant quantization distortion. The proposed hybrid receiver defines unreliable signal thresholds by statistical analysis and selectively takes additional digital equalization to save potentially increasing dynamic power consumption in digital. Simulation results report that the hybrid receiver saves at least 64% of digital equalization power with 3-tap FFE PAE in 12.5Gb/s data rate and up to 46dB loss channels. Finally, this work shows the use of embedded-DFE ADC in the hybrid receiver is limited by error propagation.Item Ultrasound-modulated optical tomography for biomedical applications(Texas A&M University, 2004-11-15) Li, JunI experimentally studied ultrasound-modulated optical tomography, which holds the promise for biomedical diagnosis. I measured the degree of polarization of laser speckles generated by scattered light transmitted through turbid media, investigated three signal-detection schemes for extracting the intensity of the ultrasound-modulated light, carried out experiments to image thick biological-tissue samples, and studied two techniques providing resolution in the cross-sections containing the ultrasonic axis. The study of degree of polarization presented results important for the understanding of polarization phenomena in turbid media. I explored an optical-filtering based signal detection scheme, improved the parallel-lock-in speckle detection scheme and proposed a speckle-contrast detection scheme. With the speckle-contrast detection scheme, I successfully obtained images of biological-tissue samples up to 50 mm thick. Further I studied frequency-swept ultrasound-modulated optical tomography for sub-millimeter resolution imaging, and developed ultrasound-modulated optical computed tomography that was based on a back-projection image reconstruction method and obtained clear images of biological-tissue samples.